1. Field of the Invention
The present invention relates to a target object detection system, which detects a presence of a target object and measures a position of the detected target object.
The present invention, more specifically, relates to a target object detection system, which detects a presence of a target object within a surrounding area of a detection apparatus, and which measures a direction and distance of the detected target object on the basis of the position of the detection apparatus.
2. Description of Relevant Art
In recent years, an apparatus, which detects a presence of a target object within a specific area and measures the position within the specific area of the detected target objects, and the method thereof have been developed.
As an example of these conventional apparatus, apparatuses disclosed in Japanese unexamined patent publications, such as JP2002-307338, JP2003-91678, and JP2002-98749, have been discovered.
The apparatus disclosed in JP2002-307338 detects a presence of a target object by checking whether or not an infrared radiation from the target object is sensed by an infrared sensor (human sensor).
The apparatus disclosed in JP2003-91678 detects a presence of a target object using a plurality of detectors which are disposed within a specific area, and the position of the detector which sensed the target object is regarded as the position of the target object.
The apparatus disclosed in JP2002-98749 detects a presence of a target object using a plurality of transmitters, which are disposed within a specific area, and a transmitter, which is provided on a target object. In this apparatus, field intensity of radio wave transmitted from the target object's transmitter and field intensity of radio wave transmitted from the transmitter provided within the specific area are computed, and the position of the target object is measured using these computed field intensities.
In the case of JP2002-307338, however, the detection of the target object can be achieved only when the target object is within a detectable range of the infrared sensor (human sensor). That is, if the target object is out of the detectable range, the detection of the target object cannot be achieved.
In the case of JP2003-91678 and JP2002-98749, following defects exist. (1) Since a plurality of detectors or transmitters are required for detecting a target object, the cost of the apparatus becomes high; (2) If a target object moves around the wide range, the detection of the target object can be achieved only when the target object is within a specific area where detectors and transmitters are provided; and (3) Rough position of the target object can be measured but the accurate position of the target object, such as a direction and distance from the detector (transmitter), cannot be measured.
If at least one of the target object and the detector is a mobile object, for example, the area where the detector is provided for detecting the target object changes continuously. In this case, the apparatus disclosed in these references lack the effectiveness in the detection of the target object. This is because it is difficult to predict the area where target object moves around and to provide a plurality of detectors (transmitters) beforehand.
Therefore, the apparatus, which can detect the presence of the target object and measure the position of the target object without causing the above described defects, has been required.
In the above described references, additionally, the power of the transmitter, which is provided on the target object for detecting the target object, has to be turned on continuously. Therefore, the conventional transmitter has a significant scope to be improved in the power consumption.
In the above described references, furthermore, the following defects have arisen: if reflected wave due to an obstacle or a wall of buildings is received in the communication between the target object and the detector, the accurate position of the target object cannot be measured; and if a plurality of transmitters is used, the detection error of the signal due to the interference of radio waves from the transmitter has arisen.
Therefore, the apparatus, which can detect the presence of the target object and measure the position of the target object without causing the above described defects, has been required.